الفهرس 
INTRODUCTION AND GROUNDING BASICSOnly 14 pages are availabe for public view
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Abstract
Grounding plays an important role in the safety and protection of the electric power system, as it provides path to the short circuit fault current that operate protection system relays. It protects the human body from the hazard shocks during the fault duration. Grounding protects the equipment of power system from damage due to a very high voltage of lightning strike or switching surge.
For the grounding to perform its tasks in the power system, its value must be very small as possible especially in the AC substations. Standard IEEE put the considerations and the calculation of the designing procedures of the grounding grid.
There are many researches to construct grounding grid in small area like GIS substation, that construct the grounding grid in foundation concrete to obtain the lowest value of the grounding grid resistance. That can be achieved by bars already found in GIS constructed hall. But in some cases the soil itself can cause problem like rocky soil, as its resistivity is very high and it is difficult to dig in deep depth, so we use vertical grid. But in some cases it is easy to dig in the soil but the features of the soil can cause problems like dry soils or high salinity soils.
In dry soil we can construct grounding grid with chemical electrodes, that the tubes in the vicinity can feed the soil beside the electrodes with water periodically due to leaching the water away from the electrode.
In high salinity soils, although it has low resistivity, but it is a corroded soil and any grounding grid found in this type of soil can be easily corroded after few years, even if it constructed from copper that has high resistance against corrosion. There are many solutions that were developed in the last few years to solve this problem, but the main idea of these solutions is to isolate the soil that grounding grid constructed in from the surrounded soil. The first solution is bentonite clay that has the ability to retain water. It is non corrosive. Its low resistivity is due to its electrolytic process between water and oxides of Sodium, Potassium and Calcium. When water is added, it swells up thirteen times of its initial volume. But we must take care that this solution is not practicable in very dry soil because bentonite clay in this case may shrink away from the electrode. The second and cheaper solution is using the cement blended with carbon. It also isolates the grounding grid from its adjacent corrosive soil. In this case we use vertical grid with main copper bar and auxiliary copper bars.
The entire cables shield must be grounded to avoid the effect of induced voltage. All the metallic pipes must be grounded especially that go out substation fence to avoid the effect of transferred voltage
In other case, the main grounding grid resistance value within its acceptable limits but the connection between conductors of the grid is not tied well; this can be occurred due to passing high fault current or cutting due to mechanical process. In these cases, the ground resistance in this point will rise dramatically, so all the connection points in the grid must be measured periodically especially the important connections like the connection between the arrestor earth terminal and grounding grid. The most used type of connection is pressure type that produce mechanical bond between conductor and connector by means of crimping using hydraulic or mechanical pressure.
In the design, we must take in account that electrical power system that can be so expanded that the short circuit’s fault current changes. One of the most important things is that the grounding grid must be tested and maintained on regular time to avoid any problems that may occur in the future.